About

『 』 (『 』, kūhaku, lit. "blank") is the online game username and account shared by Sora (空) and Shiro (白). It has became an urban legend in the real world for holding the top score of over 280 games without having any recorded losses or defeats. After Sora and Shiro were called to Disboard by Tet, they used the name to refer to themselves, and the urban legend became a legend.
『 』 is generally depicted by four game accounts, the main account being named 『 』, and the others named 『 SUB01』, 『 SUB02』, and 『 SUB03』, with Sora and Shiro controlling two accounts each.

Note, that kanji for kūhaku (空白) is a compound made of kanji from names of both protagonists: Sora (空) and Shiro (白), which is probably how the name originated.